1. Field of the Invention
The present invention relates to a backlight module, and more specifically, to a backlight module for disposing a light emitting unit on a light entrance surface tilted relative to a light exit surface or a bottom reflection surface of a light guide plate at the same side surface.
2. Description of the Prior Art
Since liquid crystal molecules do not produce light themselves, a common method for driving a liquid crystal display device to display images involves utilizing a backlight module to provide light with sufficient brightness and uniform distribution to the liquid crystal display device. Therefore, a backlight module is one of the major components of a liquid crystal display device.
Please refer to FIG. 1, which is a side view of a backlight module 10 according to the prior art. The backlight module 10 includes a light guide plate 12, a light emitting unit 14, and a reflection cover 16. The light guide plate 12 has a light entrance surface 18 and a light exit surface 20. The light emitting unit 14 is disposed on the light entrance surface 18, and the reflection cover 16 covers the light emitting unit 14. Accordingly, light emitted by the light emitting unit 14 is incident into the light guide plate 12 via the light entrance surface 18 directly or by reflection of the reflection cover 16, and then is emitted out of the light guide plate 12 via the light exit surface 20, so that the light guide plate 12 can provide light with sufficient brightness and uniform distribution to a display panel disposed thereon (not shown in FIG. 1). As shown in FIG. 1, the section of the light guide plate 12 corresponding to the light entrance surface 18 has a gradually-increased thickness so as to make the area of the light entrance surface 18 greater than that of the light emitting area of the light emitting unit 14. In such a manner, efficiency of the backlight module 10 in use of light emitted by the light emitting unit 14 can be improved.
However, since the said design causes a structure with a gradually-increased height (e.g. an inclined surface 22 as shown in FIG. 1) formed between the light exit surface 20 and the light entrance surface 18 of the light guide plate 12, light incident into the light guide plate 12 via the light entrance surface 18 may be emitted out of the light guide plate 12 via the inclined surface 22 so as to cause a hot line problem or a light leakage problem. Furthermore, as shown in FIG. 1, since the backlight module 10 needs an additional containing space formed between the light entrance surface 18 of the light guide plate 12 and the reflection cover 16 for containing the light emitting unit 14, the overall width of the backlight module 10 is increased accordingly, so as to be disadvantageous to narrow a side frame of a liquid crystal display device where the backlight module 10 is installed.